Exchange of information: states must obtain and share tax-relevant data while protecting confidentiality and limited exceptions apply Article 26 requires competent authorities to exchange tax information, including documents or certified copies, necessary for administering and enforcing domestic tax laws and the Agreement; exchanged information must be kept confidential and used only for tax assessment, collection, enforcement, appeals or oversight, unless both States' laws permit other uses with supplying authority consent. Limits include no obligation to alter domestic law or administrative practice, to provide unavailable information, or to disclose trade secrets or information contrary to public policy, while requested States must use their information-gathering measures and cannot refuse solely because information is held by banks, nominees or fiduciaries.